Paint or similar coating compositions such as lacquers, varnishes or wood stains, is used by both the skilled professional decorator and the relatively unskilled do-it-yourself painter for a variety of reasons. Typically, these are to brighten up the surroundings and/or to match the color of a particular item of furniture, floor or wall covering, and other surfaces found in buildings. As consumers have become increasingly sophisticated and individual in their choice of colors, the demand for a wider range of colors has also increased.
This presents a problem to the paint manufacturer and the retailer or trade store keeper as the former has to produce many colors in small amounts, thus losing the economies of scale and, of course the retailer or store keeper has to provide additional space to store and display this plurality of colored paints. A typical paint would be architectural paint used on site at ambient temperatures.
Some paint manufacturers have addressed this problem by developing tinting machines. These operate on the basis that a variety of colors can be made by adding colorant to a factory produced base paint at the retailer's premises. Such machines are referred to as “in-store tinting machines”. The term “in-store” is used herein to indicate a relation with small trade stores and retail outlets, in contrast to producing such coating compositions in a paint processing plant. A small number of different colored base paints, comprising three or four spanning the range of light to deep shades, is provided by the supplier to the retailer, in paint containers. Such a base paint is unfinished from the point of view of the final color.
The colorant to be added is usually in the form of pigments, pigment concentrates, tinters or dyes. Usually, about twelve to sixteen such colorants are required to produce a significant color range of paints, although only frequently three or four are required to produce any given color. The colorants are added to the base paint according to a predetermined recipe, being one of many, stored in a computer. The recipe also indicates which of the base paints should be selected for tinting in order to produce the required color.
Such tinting machines typically comprise a number of reservoirs containing the colorants, a means of delivering the colorant to the container with base paint, for example by one or more manual or automated piston or gear pumps, storage means for the collection of recipes, and control means (manual and/or computerized) for controlling the delivery of colorant in accordance with the selected recipe. The control means may, for example, control the addition of colorant by governing the traverse of pistons in pumps or by activating the pumps for a predetermined time period so that a predetermined volume of colorant is delivered in accordance with the recipe for the selected color. In this way, varying amounts of each colorant may be added to the selected base paint enabling paints of a variety of alternative colors to be produced. Finally, the base paint and added colorant are subjected to mixing, usually by intense shaking, to obtain a homogeneous mixture of base paint and colorant with even color.
Thus, it will be appreciated that the number of different colors that can be produced is determined by the number of different colorants present in the tinting machine, and the number of different base paints. Increasing the number of different colorants and/or the number of base paints will enable a greater number of different colors to be produced.
Known tinting machines have a plurality of colorant reservoirs, each reservoir having its own nozzle from which colorant is dispensed into the base paint. It would be desirable to reduce the complexity of tinting machines to have a single nozzle through which all colorants can be dispensed into the base paint. The problem, however, with using a single nozzle is that the nozzle becomes contaminated with residues of all colorants that pass through. Contamination of the nozzle results in the residual colorants being added to the base paint in a subsequent tinting operation, and therefore the final color of the paint will be incorrect. Therefore, if a single nozzle for a plurality of colorants would be used, a cleaning operation between different tinting operations would be needed.
International application WO99/32205 describes a dispensing machine for metered delivery of fluid products wherein metered quantities of colorants and base paint are fed to a mixing turbine in a dispensing head with a single dispensing nozzle (outlet) and then dispensed into a paint container through the dispensing nozzle. After each dispensing operation, the dispensing head including the mixing turbine and the dispending nozzle are washed with a pressurized solvent that is provided by a washing unit. In the dispensing machine of WO99/32205, rinsing of the dispensing head requires a relatively large volume of cleaning fluid.
It would be desirable to provide a tinting machine with a dispensing head and nozzle that could be cleaned from residual colorants without the need for large amounts of cleaning fluid.